A valve that opens and closes a fluid flow path by vertically moving a plug-type (rod-like) valve element within a valve chamber has been known as one of conventional valves for handling fluids such as chemicals. Examples of the opening/closing valve include a manual valve that opens and closes a valve element by manual operation, and a pneumatic control valve (pneumatic on-off valve) that is provided with an actuator operated by pneumatic pressure so as to enable remote operation as disclosed in, for example, PTL 1 below. Examples of the pneumatic control valve include a pneumatic control valve of normally open type in which a valve is opened when no pneumatic pressure is supplied, and a pneumatic control valve of normally closed type in which a valve is closed when no pneumatic pressure is supplied depending on a difference in a pressure application direction from a pneumatic actuator on a piston and an urging direction by a spring member, or the like.
The aforementioned pneumatic control valve includes an actuator operated by pneumatic pressure, and opens and closes a fluid flow path by vertically moving a plug-type valve element within a valve chamber. The fluid flow path includes an inlet-side flow path that brings into communication the valve chamber formed in a valve body and a flow path inlet, and an outlet-side flow path that communicates with a flow path outlet via a vertical portion extending downward from a bottom surface portion of the valve chamber.
When the aforementioned pneumatic control valve is of normally open type, a spring member that upwardly urges the valve element so as to hold a fully open position is also provided at a stem portion. To close the pneumatic control valve, pneumatic pressure is supplied to a pressure receiving surface of the actuator so as to generate a downward force larger than the urging of the spring member.
The aforementioned pneumatic control valve further includes a diaphragm that is provided so as to separate the valve chamber in which a fluid flows and an opening/closing mechanism in a liquid-tight manner. The diaphragm separates the valve chamber that forms a space in which the valve element is vertically moved and communicates with the inlet-side flow path and the vertical portion to define a portion of the flow path in which a fluid flows, and an accommodation space for the stem portion that is formed above the valve element so as to couple the valve element to the actuator, place the spring member, or the like. The diaphragm prevents a coagulable fluid such as a slurry chemical from flowing into the opening/closing mechanism of the valve element.
The conventional pneumatic control valve has such a structure that casing bodies divided into, for example, the valve mechanism side and the actuator side are integrally coupled together by vertically tightening a plurality of bolts arranged at equal intervals so as to prevent leakage.